1. Field of the Invention
The present invention relates to a paper size detecting apparatus for detecting the size of recording paper accommodated selectively in a cassette case so as to be supplied to a recording system.
2. Description of the Related Art
As is known, among recording systems there are those that employ sheet paper as recording paper.
With this type of recording system, it is common to use a cassette case for supplying recording paper in correspondence with a recording operation.
There are a plurality of paper sizes with respect to the recording paper accommodated in the cassette case, and in order to effect an accurate recording operation, it is necessary to accurately detect the size of the paper accommodated in the cassette case on each such occasion.
A typical paper size detecting apparatus used for this purpose is generally arranged as shown in FIGS. 14a and 14b.
Here, FIG. 14a shows a structure of essential portions of a mounting surface of a cassette case 1 with the cassette case 1 loaded in a recording system. FIG. 14b is a cross-sectional view of the structure of the essential portions taken along the line I--I of FIG. 14a.
In FIGS. 14a and 14b, recording paper of any one of a plurality of paper sizes is selectively accommodated in the cassette case 1.
A detection piece holder 11 is formed integrally with a case body at a predetermined position on the mounting surface of the cassette case 1, and a detection piece 12 is secured therebelow by means of a screw 13 with one end retained by the detection piece holder 11.
The detection piece 12 has a tongue 120, and included among its configurations are those shown in FIGS. 14a and 14b, as well as FIGS. 15a to 15c.
The configurations of detection pieces 12A-12C shown in FIGS. 15a to 15c correspond to configurations as viewed in the direction of arrow II of FIG. 14a when they are mounted on the cassette case 1.
In FIGS. 15a to 15c, the detection pieces 12A, 12B, and 12C are respectively provided with tongues 120A, 120B, and 120C projecting perpendicularly from their mounting surfaces when they are mounted on the cassette case 1, and their configurations are different, respectively.
The configurations of these tongues 120A, 120B, and 120C correspond to the sizes of the recording paper that can be accommodated in the cassette case 1. For instance, the detection piece 12A has a length corresponding to the JIS (Japanese Industrial Standards) A4 size in the horizontal direction of FIG. 15a. In a similar manner, the detection pieces 12B and 12C have lengths corresponding to JIS B5 and A5 sizes, respectively.
In actual application, as for these detection pieces 12A, 12B, and 12C, those each provided with a tongue of the length corresponding to the size of the recording paper to be accommodated in the cassette case 1 are selected. These detection pieces are mounted on the cassette case 1 by means of the screw 13 in each case.
As recording systems in which the cassette case 1 is loaded, for instance, facsimile machines, copying machines, and the like are conceivable.
A sensor 14 is provided on the main body of such a recording system at a position where the tongues 120A, 120B, and 120C of the detection pieces 12A, 12B, and 12C are opposed to the main body when the cassette case 1 is loaded (see FIGS. 14a and 14b).
The sensor 14 is constituted by, for instance, a transmission-type photosensor.
In the example shown in FIGS. 14a and 14b, the sensor 14 is constituted by a plurality of pairs of light-emitting elements 14A and light-receiving elements 14B that are juxtaposed at predetermined intervals in such a manner as to sandwich the tongue 120 of the detection piece 12 on the mounting surface of the cassette case 1 when the cassette case 1 is loaded in the recording system.
This sensor produces a signal corresponding to, for instance, "0" when the tongue 120 of the detection piece 12 is present between the light-emitting element 14A and the light-receiving element 14B, and produces a signal corresponding to "1" when it is absent therebetween.
As a result, sensor signals are obtained from the sensor 14 in correspondence with the configuration of the tongue of the detection piece 12 mounted on the cassette case 1 at that time, as shown in the table of FIG. 16.
These sensor signals respectively correspond to the paper sizes listed in the left-hand column of the table of FIG. 16 on a one-to-one correspondence basis.
Accordingly, if these sensor signals are introduced to and processed by an unillustrated detection circuit, it is possible to detect the size of the recording paper presently accommodated in the cassette case 1.
With the paper size detecting apparatus in which the detection piece corresponding to the size of the recording paper is used by being replaced on each such occasion, the detection pieces are required for the respective sizes of the recording paper that can be accommodated in the cassette case 1, so that the number of the detection pieces unavoidably increases as the number of paper sizes to be detected increases.
Even in cases where the paper sizes are detected within a range which does not practically cause inconveniences, the number of detection pieces corresponding to the paper sizes shown in FIG. 16 is generally considered to be a minimum requirement.
In addition, with the above-described apparatus in which the detection piece is replaced by removing the screw each time when the recording paper to be accommodated in the cassette case is replaced, the operation of replacing the detection piece has been inevitably troublesome.
At that time, only one detection piece can be mounted on the cassette case, and the remaining ones are left as they are without being used, so that the management of the detection pieces not in use has been difficult and there are even many cases where they are possibly lost.
In addition, the fact that the number of the detection pieces is large means that the number of cases where the detection piece is erroneously mounted on the cassette case increases by that margin.
Furthermore, with this type of paper size detecting apparatus, as the number of paper sized to be detected increases, there arises the need to form tongues having corresponding configurations for the respective detection pieces.
For this reason, detection pieces having tongues of sufficiently large configurations have been required to cope with the processing of the detection pieces, so that the tendency of the detection pieces to become large in their structure has been unavoidable.